• Main Authors: DARCILÉA F. CASTRO, PAULO E. DE OLIVEIRA, DILCE F. ROSSETTI, LUIZ C.R. PESSENDA
• Format: Article
• Language: English
• Published: Academia Brasileira de Ciências 2013-03-01
• Series: Anais da Academia Brasileira de Ciências
• Subjects: padrões vegetacionais; clima; Quaternário tardio; paleoambiente; Ilha do Marajó; Amazônia Oriental; vegetation pattern; climate; late Quaternary; paleoenvironment; Marajó Island; northeastern Amazonia
• Online Access: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652013000100035

The main goal of this study was to reconstruct the Late Pleistocene-Holocene floristic composition in an area of the northern Brazilian Amazonia, comparing the results with other Amazonian localities in order to discuss the factors that have influenced phytophysiognomic changes over this time period. The work in eastern Maraj&#243; Island at the mouth of the Amazonas River was approached based on analysis of 98 pollen and diatom samples from core data distributed along a proximal to distal transect of a paleoestuarine system. The results indicated high concentration of Rhizophora, associated with arboreal pollen grains typical of the modern Amazonian rainforest during the last 40,000 cal yrs BP. Pollen composition also included wetland herbs. Diatoms were dominated by marine and fresh water taxa. Wetland forest, mangrove and, subordinately herbs remained constant during most of the latest Pleistocene-early/middle Holocene. At 5,000 cal yrs BP, there was a distinguished change from forest and mangrove to wet grassland savanna due to sea level fluctuation. As marine influence decreased, the estuary gave rise to fresh water lacustrine and swamp environments, with establishment of herbaceous campos. A main conclusion from this study is that solely the occurrence of herbaceous savanna can not be used as a definitive indicator of past dry climates in Amazonian areas.<br>O objetivo deste estudo foi de reconstruir a composi&#231;&#227;o flor&#237;stica do Pleistoceno Tardio-Holoceno em uma &#225;rea da Amaz&#244;nia Oriental, comparando os resultados com outras localidades amaz&#244;nicas, a fim de discutir os fatores que influenciaram as mudan&#231;as fitofision&#244;micas. O trabalho no leste da Ilha do Maraj&#243;, na desembocadura do rio Amazonas, baseou-se na an&#225;lise de 98 amostras de p&#243;len e diatom&#225;cea derivadas de dados de testemunhos de sondagem distribu&#237;dos ao longo de um transecto proximal-distal de um sistema paleoestuarino. Os resultados indicaram alta concentra&#231;&#227;o de Rhizophora, associada a gr&#227;os de p&#243;len t&#237;picos da floresta Amaz&#244;nica moderna durante os &#250;ltimos 40.000 yrs BP. A composi&#231;&#227;o palinol&#243;gica tamb&#233;m incluiu ervas de &#225;reas alagadas. Diatom&#225;ceas s&#227;o dominadas por t&#225;xons marinhos e de &#225;gua doce. Floresta inundada, mangue e, subordinadamente erva, permaneceram constantes durante grande parte do Pleistoceno Tardio-Holoceno inferior/m&#233;dio. A 5.000 cal BP, houve mudan&#231;a marcada de floresta e mangue para savana de gram&#237;neas de &#225;reas alagadas devido a flutua&#231;&#245;es do n&#237;vel do mar. Com diminui&#231;&#227;o da influ&#234;ncia marinha, o estu&#225;rio foi substitu&#237;do por ambientes de lago de &#225;gua doce e p&#226;ntanos, com estabelecimento de campos herb&#225;ceos. Uma conclus&#227;o principal deste estudo &#233; que a ocorr&#234;ncia de savana herb&#225;cea n&#227;o pode ser usada como indicador para sugerir climas secos passados em &#225;reas amaz&#244;nicas.